MEASUREMENTS OF STRAIN AROUND DEFECTS IN SYNTHETIC DIAMONDS. Moreton Moore and Grzegorz Kowalski, Department of Physics, Royal Holloway University of London, Egham, TW20 0EX, England

Large synthetic single-crystal diamonds can be grown under conditions of high pressure and high temperature by the reconstitution technique [1], which are used in a variety of industrial applications; but they often contain defects. Crystals up to 4x4x2 mm3 in size, which had been grown in either the [001] or the [111] direction, were studied by a combination of rocking-curve analysis and x-ray topography in symmetric (+,-) Bragg-Bragg diffraction geometries, using synchrotron radiation ( = 0.1 nm). By recording series of topographs in all four principal azimuths (chi = 0, 90, 180, 270), variations in relative lattice parameter (delta a/a0) were distinguished from misorientations. The strains associated with various types of defect were measured: (a) in populations of small inclusions (of diameter 1-5 micron) dispersed in diamond matrix; (b) across growth-sector boundaries separating sectors containing different concentrations of impurities; and (c) close to relatively large (100m diameter, 1 mm long) cylindrical metal inclusions with axes along <110> directions. Rocking curves were recorded from small specimen areas selected by a translatable pin-hole in order to determine the extent of the strains and to calculate strain gradients. The various types of defect gave characteristic measurements for delta a/a0 falling in the range 6-36 parts per million and for misorientations in the range 4-40 arc seconds [2,3].

[1] R.C.Burns & G.J.Davies, in The Properties of Natural & Synthetic Diamond, edited J.E.Field (London: Academic Press), p.409, 1990.

[2,3] G.Kowalski, M.Moore, G.Gledhill & Z.Maricic, J.Phys.D:Appl. Phys. 29 (1996)1; and Diamond & Related Materials, (1996).